Magoo's Private War(1957)

The near-sighted Mr. McGoo takes his duties as an Air Raid Warden, in the civil-defense, cold-war/iron curtain days of the 1950s, seriously. When he stumbles across the premiere of a new science-fiction movie at a theatre, he thinks his town has just been invaded by outer-space aliens. He takes the on-screen activities as part of the attack and goes through all the civil-defense steps to save the audience.